A blowing technique, in which the shape of the container is achieved by blowing a hot gas into a deformable gob of molten glass in order to impart a given shape to it, is normally used for manufacturing glass containers.
For various reasons a pressing process in which the deformable molten glass is placed in a molding cavity defined by a die and a punch and adopts the shape of that cavity can be preferred to this blowing process for a variety of reasons. In particular the pressing process makes it possible to manufacture wide-mouthed containers.
One of the difficulties associated with the pressing process lies in the difficulty of producing a variety of internal shapes for the container. These internal shapes may be used to personalize the container, and to give it a strong identity. Another advantage is that containers having the same external appearance but differing in internal volume can readily be produced. Another advantage may for example also be to produce a container whose shape is optimized for its operating conditions using less material, and thus at lower cost. An internal shape may for example be produced in locations where the mechanical strength of the container is largely sufficient. Making such shapes may be difficult, because owing to the fact that the die must be removed from the forming vessel it is preferable for the die to be of a tapering or cylindrical shape in order to avoid any risk of damaging the glass when the die is removed.
One example of an embodiment which makes it possible to produce shapes in relief within a jar is to produce grooves which extend along the axis along which the die is removed. In such a situation the glass material which is being shaped does not prevent the die from being removed.
In order to form a relief within a container using a molding process it is necessary to use a punch comprising a movable system, as is for example suggested in FR 2 975 988. This punch can adopt two configurations, one in which the marking portion prints the relief, but in which the punch cannot be removed, and one in which the marking portion is retracted so that the punch can be removed.
Although such a process is of great advantage, in particular for forming deep interior shapes within a jar, practical implementation is limited because of the extremely high temperatures to which the system is subjected, which give rise to difficulties in the manufacture of a movable system which is reliable over time.
Yet another option is to remove the punch by screwing. Such screwing is described in FR 2 153 382. In this embodiment the punch is withdrawn through a helical movement, which makes it possible to form a helical shape in relief within a jar. One of the limitations of this embodiment is however that it can only be used to form helical shapes.
By way of anecdote mention may also be made of U.S. Pat. No. 4,072,491, which describes the manufacture of a “helical” shape by axial withdrawal of the punch. This is in fact a false helix, without zones of glass material which are likely to prevent axial withdrawal of the die, which is only possible because of the highly tapering shape of the inside wall of the jar. The helix is therefore made in the tapering wall of the container, but the outer wall of the container narrows uniformly between these two extremities.
This document provides a method for producing glass containers by pressing which makes it possible to use many possible forms of internal relief without resorting to mechanisms which are exposed to very high temperatures.